ILX Lightwave LDC-3916558 User Manual
User’s Guide
3A Current Source TE Module
LDC-3916558
ILX Lightwave Corporation · P. O. Box 6310 · Bozeman, MT, U.S.A. 59771 · U.S. & Canada: 1-800-459-9459 · International Inquiries: 406-556-2481 · Fax 406-586-9405
ilx.custhelp.com · www.ilxlightwave.com
70033202 June 2005
TABLE OF CONTENTS
Table of Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i
Safety and Warranty Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
Safety Information and the Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
General Safety Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
Safety Symbols. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi
Safety Marking Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi
Warranty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii
Comments, Suggestions, and Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix
Chapter 1 Introduction and Specifications
Product Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Initial Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Installing the Module into the LDC-3916 or LDC-3908 Mainframe . . . . . . . . . 2
Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Chapter 2 Operations
Connecting to the Temperature Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
TEC Grounding Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Operating the Temperature Controllers from the Front Panel . . . . . . . . . . . . 7
General Front Panel Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Example Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Choosing Control Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Setting Gain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Setting Sensor Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
LDC-3916558 i
TABLE OF CONTENTS
Setting Safety Limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Default Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
TEC Error Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Chapter 3 Remote Operations
Remote Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
LDC-3916558 3-AMP Temperature Control Module Command Set . . . . . . 19
LDC-3916558 3-Amp Temperature Controller Often Used Commands . . . . 21
Command Timing and Completion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Status Reporting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Status Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Output Off Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Error Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Chapter 4 Command Reference
GPIB Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
LDC-3916558 Device-Dependent Commands . . . . . . . . . . . . . . . . . . . . . . . . . 33
Chapter 5 Troubleshooting
Calibration Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
Recommended Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
Local Calibration of the 3916558 3-Amp Temperature Controllers . . . . . . . . 69
Thermistor Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
ITE Current Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
TE Voltage Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
Remote Calibration of the 3916558 3-Amp Temperature Controllers . . . . . . 72
Thermistor Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
ITE Current Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
TE Voltage Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
Troubleshooting Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
ii LDC-3916558
LIST OF FIGURES
Figure 2.1 Rear Panel TEC Connector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
Figure 2.2 3916 Front Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
Figure 2.3 Channel Menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Figure 2.4 TEC p1 Menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
Figure 2.5 TEC p2 Menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
Figure 2.6 TEC p3 Menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
Figure 2.7 TEC p4 Menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
Figure 2.8 Example Thermistor Resistance vs. Temperature . . . . . . . . . . . . . . . . . .14
Figure 3.1 LDC-3916558 3-Amp Temperature Controller Command Path Structure20
Figure 3.2 LDC-3916558 Status Condition Registers . . . . . . . . . . . . . . . . . . . . . . . .23
Figure 3.3 LDC-3916558 Event Status Registers . . . . . . . . . . . . . . . . . . . . . . . . . . .24
Figure 4.1 Command Description Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33
LDC-3916558 iii
LIST OF FIGURES
iv LDC-3916558
LIST OF TABLES
Table 2.1 TEC Controllable Laser Sources . . . . . . . . . . . . . . . . . . . . . . . . . 11
Table 2.2 3916558 Default Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Table 2.3 TEC Error Indicators. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Table 3.1 LDC-3916558 Often Used Commands. . . . . . . . . . . . . . . . . . . . . 21
Table 3.2 LDC-3916558 TEC Output Off Register Contents . . . . . . . . . . . . 25
Table 4.1 LDC-3916 Device-Dependent Commands . . . . . . . . . . . . . . . . . . 30
Table 5.1 Recommended Test Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . 68
Table 5.2 Required Calibration Components . . . . . . . . . . . . . . . . . . . . . . . . 68
LDC-3916558 v
LIST OF TABLES
vi LDC-3916558
CHAPTER 1
INTRODUCTION AND SPECIFICATIONS
This chapter is an introduction to the LDC-3916558 3-Amp Temperature Control
Module for the LDC-3916 or LDC-3908 Laser Diode Controller Mainframe. It
contains unpacking information, instructions on how to install and apply power,
and safety considerations and instructions. It also contains some maintenance
information and specifications.
If any of the following symptoms exist, or are even suspected, remove the LDC-3916558
Module from service. Do not use the module until trained service personnel can verify
safe operation.
Visible damage
Severe transport stress
Prolonged storage under adverse conditions
Failure to perform intended measurements or functions
If necessary, return modules to ILX Lightwave for service and repair to ensure that safety
features are maintained.
Product Overview
The 3916558 module is intended to be used within a LDC-3916 16-channel or
LDC-3908 8-Channel Laser Diode Controller Mainframe. The module contains a
single three ampere independent temperature controller that drives a
thermoelectric cooler (TEC). The temperature controller features a bi-polar
current driver that works with most TEC modules to deliver precise temperature
control over a wide range of temperatures. The temperature controller operates
using thermistor type temperature sensors only. The LDC-3916558 features a
LDC-3916558 1
CHAPTER 1
INTRODUCTION AND SPECIFICATIONS
Installing the Module into the LDC-3916 or LDC-3908 Mainframe
TEC module voltage measurement, selection of thermistor current range, and
control loop gain adjustment from 1 to 127.
Initial Inspection
When you receive your LDC-3916558 3-Amp Temperature Control Module, check
for shipping damage immediately. Verify that the module has an ESD protective
hood on the 15-pin D-sub and that it is enclosed in an ESD safe handling bag.
Remember before handling the module to follow proper ESD safe handling
procedures.
Installing the Module into the LDC-3916 or LDC-3908
Mainframe
If you are receiving this new module without an LDC-3916 or LDC-3908
Mainframe for installation into a previously purchased mainframe, follow the
instructions below. If your system was configured at the factory with your desired
modules, skip this section.
Static discharge can damage your new Temperature Controller Module. Be certain you
use proper grounding procedures before you unpack and install your module(s) into the
LDC-3916 or LDC-3908 Mainframe.
Inspect the module for any visible shipping damage that may have occurred before
inserting the module into the mainframe. Pay special attention to the copper shielding
material on the back edge of the module.
Be sure that the LDC-3916 or LDC-3908 Mainframe power is off before inserting or
removing any module.
Unwrap the module from the anti-static bag it was packaged in.
Make sure the instrument the module is going into, either the LDC-3916 or the
LDC-3908, is switched off. Insert the module into the desired slot from the rear.
Each module is supported by two plastic card guides inside of the mainframe.
Insert the module, 40-pin connector first, by lining up the edges of the module
frame with the appropriate card guides (one on top and one on the bottom).
Carefully slide the module into the mainframe slot until the connector is seated.
You will have to push a little harder to seat the module. The rear panel of the
module should be flush with the mainframe when properly inserted. Fasten the
module to the mainframe with two screws located at the top and bottom of the
module rear panel.
2 LDC-3916558
Specifications
INTRODUCTION AND SPECIFICATIONS
Specifications
CHAPTER 1
Temperature Control
Temperature Control Range2:-99
Thermistor Setpoint (Resolution and Accuracy)
-20oC to 20oC0.1
o
C to 50oC0.2
20
Short Term Stability (1 hour)
Long Term Stability (24 hours)
1
4
:<+0.007oC
5
:<+0.01oC
o
C to 150oC
3
o
C; +0.2oC
o
C; +0.2oC
Output Type: Bipolar current source
Compliance Voltage: 8 VDC
Maximum Output Current: 3 A
Maximum Output Power: 24 W
6
Current Noise and Ripple
: <2 mA rms
Current Limit Range: 0.1 to 3.10 A
Current Limit Set Accuracy: +0.05 A
Control Algorithm: Gain adjustable from 1 to 127
Temperatu re Sensor
Types: Thermistor (2-wire NTC)
7
Thermistor Sensing Current
: 10 uA/100 uA
Useable Thermistor Range: 25 to 450,000 Ω typical
User Calibration: Steinhart-Hart, 3 constants
TEC Measurement (Display)
Temperature
8
:-99.9
Range
Accuracy: +
o
C to 199.9oC
0.5oC
Thermistor Resistance (10 uA setting)
Range: 0.01 to 450.00 kΩ
9
Accuracy
:+0.05 kΩ
Thermistor Resistance (100 uA setting)
Range: 0.001 to 45.000 kΩ
10
Accuracy
:+0.005 kΩ
TE Current Range: -3.00 to 3.00 A
TE Current Accuracy: +0.04 A
08_05 LDC-3916558 3
CHAPTER 1
INTRODUCTION AND SPECIFICATIONS
Specifications
TE Current Resolution: +0.01 A
Voltage Range: -10.75 to 10.75 V
Voltage Resolution: 100 mV (1 mW through GPIB)
11
Voltage Accuracy
1. All values relate to a one-hour warm-up period
2. Software limits of range. Actual range possible depends on the physical load, thermistor type, and TEC module used.
3. Accuracy figures are quoted for a typical 10 kΩ thermistor and 100 uA cur rent setting for -5
and a 10 uA current setting for -20
are dependent upon the user-defined configureation of the instrument.
4. Over any one-hour period, half-scale output, controlling an LDM-4412 mount @ 25
5. Over any 24-hour period, half-scale output, controlling an LDM-4412 mount @ 25
6. Measured at 2A output over a bandwidth of DC to 25 MHz.
7. Thermistor current software selectable by front panel or GPIB.
8. Software limits of display range.
9. Using a 100 kΩ thermistor, controlling an LDM-4412 mount of -30
10.Using a 10 kΩ thermistor, controlli ng an LDM-4412 mount over -5
11.Voltage measurement accuracy while driving calibration load; accuracy is dependent upon load used.
:+70 mV (+20 mV through GPIB)
o
o
C to -5oC. Accuracy figures are relative to the calibration standard. Both resol ution and accuracy
o
C to 25oC.
o
C to 90oC
C to 50oC, and a typical 10kΩ thermistor
o
C, with 10kΩ thermistor, on 100 uA setting.
o
C, with 10kΩ thermistor, on 100 uA setting.
In keeping with our commitment to continuous improvement, ILX Lightwave
reserved the right to change specifications without notice or liability for such
changes.
4 LDC-3916558
CHAPTER 2
OPERATIONS
This chapter introduces you to the operation of the LDC-3916558 front panel
control functions. It shows you how to use the 3916558 to control a load
temperature. It also gives instructions for connecting a load to a temperature
controller's output. We recommend that you review the contents of this chapter at
a minimum before operating your new LDC-3916558 3-Amp Temperature Control
Module.
The 3916558 module contains a 3-Amp temperature controller.
The 3916558 is intended for use with Thermoelectric Cooler (TEC or Peltier)
modules.
Connecting to the Temperature Controller
Use the 15-pin connectors on the rear panel of your 3916558 module to make
connections to thermoelectric cooler (TEC) modules and their associated
thermistors. There are connections provided for current drive and temperature
sensor. Also provided are connections to earth ground (chassis) and to the
modules' analog ground. The pinout diagram for this connector is shown in Figure
2.1.
LDC-3916558 5
CHAPTER 2
OPERATIONS
Connecting to the Temperature Controller
1
9
2
3
4
5
6
7
8
10
11
12
13
14
15
Figure 2.1 Rear Panel TEC Connector
1,2 TE Module (+)
3,4 TE Module (-)
5,6 Earth Ground
7 Sensor (+)
8 Sensor (-)
9 Analog Ground
10 N/C
11 N/C
12 N/C
13 N/C
14 N/C
15 N/C
Current will flow from pins 1 and 2 (connected internally) to pins 3 and 4 when the
controller is trying to cool the load. This is referred to as "positive" current.
Current will flow from pins 3 and 4 to pins 1 and 2 when the controller is trying to
heat the load. Pin 5 and 6 are connected to the LDC-3916 or LDC-3908 chassis,
which is connected to "earth ground." Sensor current (10 µA or 100 µA) flows
from pin 7 to pin 8; a voltage will develop across a thermistor connected to these
pins. Analog Ground is provided at pin 9 as a convenient reference whe n making
measurements or troubleshooting a system, but it is not normally required. Pins
10-15 are reserved by ILX Lightwave for diagnostic purposes and must not be
connected.
TEC Grounding Considerations
The TEC Module pins are isolated from chassis ground, allowing either output
terminal to be connected to earth ground at the user's option.
For the TEC connector, if any one terminal pin is grounded, then no other terminal pin
should be grounded. Do NOT connect Sensor (-) to TEC Module (- or +). Damage to the
instrument and devices will occur.
6 LDC-3916558
OPERATIONS
Operating the Temperature Controllers from the Front Panel
CHAPTER 2
Operating the Temperature Controllers from the Front Panel
This section describes how to operate the LDC-3916558 3-Amp Temperature
Controller from the front panel of either the LDC-3916 or LDC-3908 mainframe. It
begins by reviewing the front panel operations and continues by showing you an
example. For a more detailed explanation of the front panel keys, see either the
LDC-3916 or LDC-3908 Mainframe manual.
General Front Panel Operation
DISPLAY AREA
SOFTKEYS
Ï
Ð
Figure 2.2 3916 Front Panel
ADJUST AREA
INC
DEC
The two areas of interest on the front panel are the DISPLAY area and the
ADJUST area. The DISPLAY area contains the display screen and various keys
that allow you to select a menu and parameters within that menu.
The keys labeled F1, F2, F3, and F4 have several functions depending which
page is displayed. The boxed text on the right of the screen are the functions
associated with these softkeys. In the lower right corner of the DISPLAY area are
the UP (K) and DOWN (L) ARROW hardkeys. Most of the menus have adjustable
parameters. You adjust the parameters using the K or L hardkeys.
08_05 LDC-3916558 7
CHAPTER 2
OPERATIONS
Operating the Temperature Controllers from the Front Panel
The ADJUST section contains
keys used to adjust the value of
Figure 2.3 Display Area
a parameter once selected. Set
the value of a parameter using
the numeric keypad (along with
the ENTER key), the ADJUST
knob, or the INC (K) and DEC (L)
keys in the lower left corner of
the ADJUST section.
Example Setup
The 3916558 temperature controller has four pages (menus) of information.
Suppose you need to maintain the temperature of a laser package at 15.5 °C .
Your laser is in a package that comes equipped with an internal TEC module and
a thermistor.
To set up the temperature controller:
• Select constant-temperature control mode
• Enter the temperature setpoint of 15.5 C
• Select the sensor current range
• Enter the appropriate thermistor constants
• Set the control loop gain
• Set appropriate high temperature limit and TEC module current limits.
To access any of the TEC information pages you must start with the "Channel"
menu. The most direct way is to press the CHAN key located directly below the
MAIN key in the upper right corner of the DISPLAY area.
The Channel menu allows you to change channels (modules) by rotating the
ADJUST knob, turn the temperature controllers on or off, and access each of the
TEC's menus. To get to the TEC's first menu, press t he F2 softkey: it is "att ached"
to the "TEC" box in the Channel menu. The next menu is the TEC page 1 menu.
Figure 2.3 Display Area
Figure 2.3 Channel Menu
8 LDC-3916558
OPERATIONS
Operating the Temperature Controllers from the Front Panel
CHAPTER 2
In the TEC page 1 menu, you can set the Temperature setpoint (TSet), the high
temperature limit (TLim), and the control mode (Mode). This page also displays
measured temperature (T), TE module current (I), and measured TEC module
voltage (V). You can also turn the controller on or off from this page.
To enter the temperature set point, press the L hardkey until the TSet pa rameter is
highlighted. Enter 15.5 using the keypad, and press Enter. Note: whenever you
use the keypad to enter a parameter value, you must press Enter within three
seconds or the parameter will revert to its previous value. Now press the L
hardkey until the TLim parameter is highlighted. Enter 40.0 using the numeric
keypad. Now press the L hardkey until the Mode parameter is highlighted. Press
the INC hardkey in the ADJUST area until "T" is displayed.
Figure 2.4 TEC p1 Menu
From the TEC page 1 menu, press the F4 softkey: it is attached to the "downarrow" box on the page 1 menu. Now you will see the TEC page 2 menu.
Figure 2.5 TEC p2 Menu
In the TEC page 2 menu, you can set the constant resistance setpoint, the
constant current setpoint, and the current limit. Press the L hardkey until the ILim
parameter is highlighted. Enter 3.0 using the numeric keypad. The RSet
parameter is for constant resistance control mode, and the ISet parameter is for
constant current mode.
08_05 LDC-3916558 9
CHAPTER 2
OPERATIONS
Operating the Temperature Controllers from the Front Panel
Figure 2.6 TEC p3 Menu
In the TEC page 3 menu, press the hardkey until the Gain parameter is
highlighted. If you're not sure what the best gain setting should be, a safe first
choice is 30. If you want the controller to drive to the setpoint faster, enter a
higher value. For this example, enter the number 35. Now press the L hardkey
until the Sensor parameter is highlighted. For now, press the INC hardkey in the
ADJUST area until 100 µA is displayed. The other parameters you can enter from
this page are the Steinhart-Hart coefficients for the particular thermistor that you
are using to measure temperature. If it's installed in a laser package, the
coefficients may be available in the package documentation. You can restore the
default values by pressing the F2 softkey. The defaults are approximate values for
the typical 10 kΩ thermistor.
From the TEC page 3 menu, press the F4 softkey: it is attached to the "downarrow" box on the page 3 menu. Now you will see the TEC page 4 menu. In the
TEC page 4 menu, you can configure the TEC to turn off a laser current source in
a different channel that has any of the modules shown in Table 2.1. The TEC will
then turn off an external laser if the temperature limit is exceeded or if the TEC
fails in anyway. Highlight the Channel parameter and turn the knob (or press the
INC hardkey) to select the desired channel number, All to choo se all channels, or
None so that the TEC will not turn off any laser current sources.
10 LDC-3916558
Figure 2.7 TEC p4 Menu
OPERATIONS
Operating the Temperature Controllers from the Front Panel
Note: The only channel numbers that will appear are channels in which a controllable laser
source resides. Next, highlight the Output parameter and turn the knob (or press the INC
hardkey) to select laser source output 1 or 2 (refer to Table 2.1), Both to choose both
outputs, or None so that the TEC will not turn off either laser current source output. In
modules with 2 laser sources, output 1 is the top source and output 2 is the bottom source.
Table 2.1 TEC Controllable Laser Sources
CHAPTER 2
3916 Module Firmware Version Number of
3916371 v2.03 or greater 1
3916372 v2.03 or greater 1
3916374 v2.03 or greater 1
3916376 v2.03 or greater 1
3916332 v1.03 or greater 2
3916334 v1.03 or greater 2
3916336 v1.03 or greater 2
3916338 v1.06 or greater 1
Laser Source
Outputs
You are now finished setting up the TEC to control temperature to 15.5 C.
Connect the load and turn on the temperature controller. From any of the three
TEC pages p1, p2, p3 or p4, you can turn on the output by pressing the F1
softkey, associated with the "OFF" box in each page. Notice that the text inside
the box changes to "ON." The text box reports the controller's on/off status.
Note: To check the firmware version in any module, select the correct channel number in
the CHAN menu, then press the following keys in this order:
+/
.
Enter
For information regarding firmware upgrades, contact ILX Customer Support.
08_05 LDC-3916558 11
CHAPTER 2
Guidelines
Choosing Control Mode
OPERATIONS
Guidelines
This section presents some guidelines intended to assist you in selecting the
optimal settings for your application.
In the preceding example, you configured a controller to maintain a load at a
constant temperature. The 3916558 controller uses a thermistor to measure
temperature. A negative temperature coefficient (NTC) thermistor is a device
whose resistance decreases as its temperature increases. The sense-curren t that
the controller provides through the thermistor results in a voltage across the
thermistor. This voltage is used as a feedback signal by the 3916558's control
loop to maintain a constant temperature.
In both constant-temperature and constant-resistance modes, the quantity that is
maintained constant by the controller is the thermistor resistance. In constant
temperature mode, the 3916558 converts the temperature setpoint to a thermistor
resistance setpoint.
The 3916558 uses the Steinhart-Hart equation to convert a temperature to a
resistance. The equation describes the nonlinear resistance vs. temperature
characteristics of typical thermistors. Calibrating a thermistor consists of
measuring its resistance at various temperatures, and fitting these measured data
to the Steinhart-Hart equation. The resulting coefficients C1, C2, and C3
effectively describe the thermistor.
If you need to know the precise temperature of your load, you must use a
calibrated thermistor, and enter its Steinhart-Hart coefficients C1, C2, and C3 in
the page 3 menu. If the exact temperature is not crucial, you can use the default
constants provided by the 3916558. However, the 3916558's temperature
accuracy specifications apply only to a calibrated thermistor with C1, C2, and C3
entered.
In effect, constant temperature control mode is the same as constant resistance
mode, but the temperature setpoint TSet is converted to a resistance setpoint.
(RSet, the constant-resistance setpoint, is not affected by TSet.) If you prefer to
avoid that conversion, or if you do not know your thermistor's coefficients, but you
know the thermistor resistance at your desired operating point, then constantresistance mode is an option for you.
Another control mode that is available in the 3916558 is constant-current mode.
In general, the amount of heat a TEC module pumps depends on its drive current.
If you have a situation where a constant heat load must be removed or added,
then you might consider using constant current mode.
12 LDC-3916558
OPERATIONS
Guidelines
CHAPTER 2
Setting Gain
The control circuit in the 3916558's temperature controller includes a
"proportional" section. The amount of current provided by this circuit is
proportional to the difference between the mea sured temperature (resistance) and
the setpoint temperature (resistance). The proportionality constant of this circuit is
the Gain setting in the page 3 menu. A higher value in this setting will cause more
current to flow when the load temperature differs from the setpoint temperature,
thus causing a quicker correction.
More gain is not always better, though, as the thermal mass of the load may
cause a situation where the load temperature oscillates about the setpoint.
Selecting the proper gain for your particular application is normally an empirical
procedure, with heat load, thermal mass, maximum current, desired settling time,
and allowable overshoot all playing a part.
A common method for selecting the gain to get the fastest temperature settling
time is the following: set the gain to 30, turn on the output and allow the load to
settle, then increase the gain until the load temperature oscillates about the
setpoint. Then decrease the gain by a few points until the oscillations cease.
The control circuit also includes an integrating section. The longer the load
temperature is different from the setpoint, the more current the integrating section
contributes. An integrating term is indispensable in a system that has inertia, such
as thermal mass. The integrating circuit is not adjustable.
Setting Sensor Current
You can select a thermistor sense current of 10 µA or 100 µA in the page 3 menu.
When deciding which current (and thermistor) to use, keep in mind the following
principles:
1 To ensure measurement accuracy, the voltage across the thermistor must not exceed 5 V.
2 To improve control responsiveness, the thermistor voltage variations that result when the
load temperature deviates from the setpoint should be as large as possible.
Using 10 A as the sense current will allow you to use a maximum thermistor
resistance of ~ 500 kΩ. The 100 µA setting allows an ~ 50 kΩ maximum.
To see why maximizing the voltage variation is an issue, refer to F igure 2.8, which
shows resistance as a function of temperature for a thermistor. The values shown
were selected for simplicity in this example, and may not reflect real thermistor
values.
08_05 LDC-3916558 13
CHAPTER 2
Ω
Ω
Ω
Ω
Ω
µ
OPERATIONS
Guidelines
5 V
4 V
3 V
2 V
1 V
Resistance
50 k
40 k
30 k
20 k
10 k
20 °C 40 °C
60 °C 80 °C
100 °C
Vth, 10
0.5 V
0.4 V
0.3 V
0.2 V
0.1 V
A Vth, 100 µA
Figure 2.8 Example Thermistor Resistance vs. Temperature
Suppose you want to use the thermistor in Figure 2.8 to control a load to 20oC. At
o
C, the thermistor's resistance is 25 kΩ. Deviations of 1oC from 20oC will cause
20
resistance variations of about 2 kΩ. If you use the 10 µA setting, there will be 20
mV of feedback to the control circuit. Using the 100 µA setting will provide 200
mV of feedback. The larger feedback signal means that the temperature will be
more tightly controlled.
14 LDC-3916558
Notice also that the lower slope of the curve at the higher temperatures results in
a smaller feedback signal. It may be necessary, if you are controlling to higher
temperatures, to use a thermistor with a different curve.
If you do not have the option of selecting a thermistor, use the following guideline:
If your desired setpoint results in a thermistor resistance of less than 50 kΩ, use
the 100 µA setting. Otherwise, use the 10 µA setting.
Setting Safety Limits
TEC modules can be damaged by excessive current, and module manufacturers
will typically specify a maximum safe operating current for their module. The
3916558 controller provides a current limit feature (ILim) that allows you to set the
maximum current that the controller will supply. The ILim setting is in the page 2
menu; its units are Amperes.
It is normal for the controller to be in current limit, especially when the load
temperature is far from the setpoint. An indication, "ILim," will appear on the
screen when the controller is in a current-limit condition.
OPERATIONS
Guidelines
CHAPTER 2
If the load you are cooling generates more heat than the controller and TEC
module can remove, the load will eventually heat up. In fact, if the TEC module's
heat sink becomes heat saturated, the TEC current may actually start heating the
load due to the resistance of the module. This situation is sometimes referred to
as "thermal runaway," and can cause a load to become damaged.
To help avoid thermal runaway damage, the 3916558's controller provides a hightemperature limit setting (TLim). When the load temperature exceeds the TLim
setting, the 3916558 will turn off the TEC current and generate an error . The TLim
setting is in the page 1 menu. Using GPIB, you can disable the high-temperature
limit from turning off the controller. See Chapters 3 and 4 for more information
about disabling or enabling conditions that will turn off the controller.
08_05 LDC-3916558 15
CHAPTER 2
OPERATIONS
Default Settings
Default Settings
When you select Default from the Recall menu, the 3916558 module will return to
the following settings:
Table 2.2 3916558 Default Settings
Output Off
Mode Constant-Temperature
Temperature setpoint (TSet) 22oC
TEC current setpoint (ISet) 1.0A
Current limit (ILim) 1.0A
Temperature limit (TLim) 80.0
Resistance setpoint (RSet) 10kΩ
Gain 3
Sensor Current 100 uA
C1 1.125 (x 10
C2 2.347 (x 10
C3 0.855 (x10
o
C
-3
)
-4
)
-7
)
TEC Error Indicators
The 3916558 Controller indicates general TEC operational error conditions.
When an error occurs, the Error Indicator Code will appear on the Status page,
the Chan page, or the respective channel's setup pages. The Error Indicator
Code will clear when you exit any page where it appears. Error Indicator codes
are summarized in Table 2.3. Some of these errors can be disabled using GPIB.
See Chapter 4 for more information.
16 LDC-3916558
OPERATIONS
TEC Error Indicators
Table 2.3 TEC Error Indicators
Error Number Error Condition Probable Cause
CHAPTER 2
E402 Open Sensor An open circuit has been detected in the
TE Module Open An open circuit has been detected in the
E403
E404 Current Limit The controller reached the current limit,
E405 Voltage Limit The output driver has reached its voltage
E407 Temperature Limit The measured temperature has reached
E409 Sensor Changed The sensor current was changed while
E410 T olerance error The output dropped out of tolerance, and
E415 Sensor Shorted The measured thermistor resistance is
E416 Temperature Conversion error The temperature setpoint could not be
thermistor connections. Check the
connections to the thermistor and to pins
7 and 8 on the 15-pin connector.
TEC module connections. Check the
wires and connections to the TEC
module, and to pins 1, 2 and 3, 4 on the
controller’s 15-pin connector.
and the “current limit” bit of the Output
Off Enable register has been set using
GPIB.
limit and the “voltage limit” bit of the
Output Off Enable register has been set
using GPIB.
the high-temperature limit setting.
the output was on, and the “Sensor
Changed” bit of the Output Off Enable
register has been set using GPIB.
the “Tolerance” bit in the Output Off
Enable register has been set.
less than 25Ω, and the “Sensor Shorted”
bit in the Output Off Enable register has
been set.
converted to a valid control setting. This
can happen if the Steinhart-Hart
constants are invalid.
E435 Mode Changed The TEC mode was changed while the
The errors that are enabled in the "Output Off Enable" register by default at
power-up are Open Sensor, TEC Module Open, Temperature Limit, and Sensor
Shorted. The Output Off Enable register is not saved at power-down.
08_05 LDC-3916558 17
TEC output was on.
CHAPTER 2
OPERATIONS
TEC Error Indicators
18 LDC-3916558
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